Submitted by: Submitted by ghosla231
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Category: Science and Technology
Date Submitted: 10/18/2016 01:50 PM
Reinforced Concrete
Nature and applications of pulverized fuel ash and superplasticizer
Pulverised fuel ash (PFA), is a waste product of pulverised fuel (typically coal) fired power stations. The fuel is pulverised into a fine powder, mixed with heated air and burned. Approximately 18% of the fuel forms fine glass spheres, the lighter of which (c. 75%) are borne aloft by the combustion process. They are extracted from the flue gasses by cyclones and electrostatic precipitation.
The resultant material is used as engineering fill and as a component for concrete. It has been widely used, particularly in the UK, for concrete block production. The blocks are lightweight and have excellent thermal insulation properties. PFA can undergo a pozzolanic reaction and become brittle over time. PFA has a fine dust texture and is grey in colour.
Superplasticizers, also known as high range water reducers, are chemical admixtures used where well-dispersed particle suspension is required. These polymers are used as dispersants to avoid particle segregation (gravel, coarse and fine sands), and to improve the flow characteristics (rheology) of suspensions such as in concrete applications. Their addition to concrete or mortar allows the reduction of the water to cement ratio, not affecting the ability of the mixture, and enables the production of self-consolidating concrete and high performance concrete. This effect drastically improves the performance of the hardening fresh paste. The strength of concrete would increase when the water to cement ratio decreases. However, their working mechanisms lack a full understanding, revealing in certain cases cement-superplasticizer incompatibilities. The addition of superplasticizer in the truck during transit is a fairly new development within the industry. Admixtures added in transit through automated slump management systems, such as Verifi, allow concrete producers to maintain slump until discharge without reducing concrete...